We present new high-resolution and high-sensitivity studies of the jets in the WAT source 3C 465, using deep transverse-resolved radio observations from e-MERLIN, and with complementary observations from the VLA. We derive a lower limit $β_{\rm j}$ = ($ν_{\rm j}$/$c$) $\gtrsim$ 0.5 for the jet speed, and an upper limit $θ_{\rm j}$ $\lesssim$ 61$^{\circ}$ for the jet angle to the line of sight. The jet spectral index ($α$, defined in the sense $S \propto ν^α$) is fairly constant (<$α_{\rm jet}$> = $-$0.7), and spectral flattening within 4.4 kpc of the core coincides with bright knots and is consistent with the site of X-ray particle acceleration at the base of the radio jet found in previous studies. There is little difference between the spectra of the two hotspot components, plausibly indicating that electron populations of the same properties are injected there. The NW and SE plumes are approximately homologous structures, with variations in mass injection and propagation in external pressure and density gradients in the two regions plausibly accounting for the slightly steeper spectrum in the NW plume, <$α_{\rm NWp}$> = $-$1.43 compared with the SE plume, <$α_{\rm SEp}$> = $-$1.38. Our synchrotron lifetime model supports plausible reacceleration of particles within the plume materials. Overall, our results show that the first-order Fermi process at mildly relativistic and non-relativistic shocks is the most likely acceleration mechanism at play in 3C 465 and distinguish differences between the acceleration at $β_{\rm j}$ $>$ 0.5 and $β_{\rm j}$ $<$ 0.5. The former case can accelerate electrons to higher Lorentz factors.
Extragalactic jets are the most powerful persistent sources of the universe. Those pointing at us are called blazars. Their relativistically boosted emission extends from radio frequencies to TeV energies. They are also suspected to be the sources of energetic neutrinos and high energies cosmic rays. The study of their overall spectrum indicates that most of the emission of powerful blazars is in hard X-rays or in soft gamma-rays. In this band we can find the most powerful jets, visible also at high redshifts. It is found that the jet power is linked to the accretion luminosity, and exceeds it…
We perform three general-relativistic magnetohydrodynamic simulations of black hole accretion designed to test how sensitive results are to grid resolution in the jet region. The cases differ only in numerics, modelling the same physical scenario of a radiatively inefficient, geometrically thick, magnetically arrested flow onto a rapidly spinning black hole. Properties inferred with the coarsest grid generally agree with those found with higher resolutions, including total jet power and its decomposition into different forms, velocity structure, nonaxisymmetric structure, and the appearance of…
The discovery by the Large Area Telescope on board Fermi of variable gamma-ray emission from radio-loud narrow-line Seyfert 1 (NLSy1) galaxies revealed the presence of a possible third class of Active Galactic Nuclei (AGN) with relativistic jets in addition to blazars and radio galaxies. Considering that NLSy1 are usually hosted in spiral galaxies, this finding poses intriguing questions about the nature of these objects and the formation of relativistic jets. We report on a systematic investigation of the gamma-ray properties of a sample of radio-loud NLSy1, including the detection of new obj…
Before the launch of the Fermi satellite only two classes of Active Galactic Nuclei (AGN) were known to generate relativistic jets and thus to emit up to the gamma-ray energy range: blazars and radio galaxies, both hosted in giant elliptical galaxies. The first four years of observations by the Large Area Telescope (LAT) on board Fermi confirmed that these two populations represent the most numerous identified sources in the extragalactic gamma-ray sky, but the discovery of variable gamma-ray emission from 5 radio-loud Narrow-Line Seyfert 1 (NLSy1) galaxies revealed the presence of a possible …
We present a survey of optical [OI] emission at 6300 Å toward 65 TTauri stars at the spectral resolution of $\sim7$ km/s. Past work identified a highly blueshifted velocity component (HVC) tracing microjets, and a less blueshifted low-velocity-component (LVC) attributed to winds. We focus here on the LVC kinematics to investigate links between winds, jets, accretion, and disk dispersal. We track the behavior of four types of LVC components: a broad and narrow component ("BC" and "NC") in LVCs that are decomposed into two Gaussians, which typically have an HVC, and the single-Gaussian LVC profi…
In recent work, we have identified two sub-populations of radio-loud AGN which appear to be distinguished by jet structure, where low-efficiency accreting systems produce `weak' jets which decelerate more rapidly than the `strong' jets of black holes accreting near the Eddington limit. The two classes are comprised of: (1) The weak jet sources, corresponding to FR I radio galaxies, having a decelerating or spine-sheath jet with velocity gradients, and (2) The strong jet sources, having fast, collimated jets, and typically displaying strong emission lines. The dichotomy in the ν_peak-L_peak pla…
According to the currently favored picture, relativistic jets in active galactic nuclei (AGN) are launched in the vicinity of the black hole by magnetic fields extracting energy from the spinning black hole or the accretion disk. In the past decades, various models from shocks to magnetic reconnection have been proposed as the energy dissipation mechanism in the jets. This paper presents a short review on how linear polarization observations can be used to constrain the magnetic field structure in the jets of AGN, and how the observations can be used to constrain the various emission models.
Relativistic magnetized jets are key elements in Active Galactic Nuclei and in other astrophysical environments. Their structure and evolution involves a complex nonlinear physics that can be approached by numerical studies only. Still, owing to a number of challenging computational aspects, only a few numerical investigations have been undertaken so far. In this paper, we present high-resolution three dimensional numerical simulations of relativistic magnetized jets carrying an initially toroidal magnetic field. The presence of a substantial toroidal component of the field is nowadays commonl…
We report that active galactic nucleus (AGN) jets are causally connected on parsec scales, based on 15 GHz Very Long Baseline Array (VLBA) data from a sample of 133 AGN jets. This result is achieved through a new method for measuring the product of the jet Lorentz factor and the intrinsic opening angle Gamma*theta_j from measured apparent opening angles in flux density limited samples of AGN jets. The Gamma*theta_j parameter is important for jet physics because it is related to the jet-frame sidewise expansion speed and causal connection between the jet edges and its symmetry axis. Most import…
We present the results of special relativistic, adaptive mesh refinement, 3D simulations of gamma-ray burst jets expanding inside a realistic stellar progenitor. Our simulations confirm that relativistic jets can propagate and break out of the progenitor star while remaining relativistic. This result is independent of the resolution, even though the amount of turbulence and variability observed in the simulations is greater at higher resolutions. We find that the propagation of the jet head inside the progenitor star is slightly faster in 3D simulations compared to 2D ones at the same resoluti…
We investigate the expected high-energy neutrino fluence from internal shocks produced in the relativistic outflow of gamma-ray bursts. Previous model predictions have primarily focussed on on-axis observations of uniform jets. Here we present a generalization to account for arbitrary viewing angles and jet structures. Based on this formalism, we provide an improved scaling relation that expresses off-axis neutrino fluences in terms of on-axis model predictions. We also find that the neutrino fluence from structured jets can exhibit a strong angular dependence relative to that of gamma-rays an…
Polarimetric measurements, especially if extended at high energy, are expected to provide important insights into the mechanisms underlying the acceleration of relativistic particles in jets. In a previous work we have shown that the polarization of the synchrotron X-ray emission produced by highly energetic electrons accelerated by a mildly relativistic shock carries essential imprints of the geometry and the structure of the magnetic fields in the downstream region. Here we present the extension of our analysis to the non-stationary case, especially suitable to model the highly variable emis…
Jetted plasma outflows from active galactic nuclei (AGN) represent the most energetic phenomena in the known universe, and play a key role in regulating galaxy formation through feedback processes. The JVLA and VLBA have played an indispensable role in understanding the physics of these powerful jets and their environments, via high angular resolution full polarization imaging and astrometric studies. By bridging the current interferometric gap between the JVLA and VLBA with intermediate baselines, the ngVLA offers exciting new opportunities to explore the intermediate regions downstream of th…
I review here the present observational efforts to study parsec-scale radio jets in active galactic nuclei with very-long-baseline interferometry (VLBI) as related to the new window to the Universe opened by the LAT instrument on-board the Fermi Gamma-Ray Space Telescope. I describe the goals and achievements of those radio studies, which aim to probe the emission properties, morphological changes and related kinematics, magnetic fields from the linear and circular polarization, etc., and I put those in the context of the radio--gamma-ray connection. Both statistical studies based on radio sur…
Active galactic nuclei, hosting supermassive black holes and launching relativistic jets, are the most numerous objects on the gamma-ray sky. At the other end of the mass scale, phenomena related to stellar mass black holes, in particular gamma-ray bursts and microquasars, are also seen on the gamma-ray sky. While all of them are thought to launch relativistic jets, the diversity even within each of these classes is enormous. In this review, I will discuss recent very high energy gamma-ray results that underline both the similarity of the black hole systems, as well as their diversity.
Extragalactic jets are a common feature of radio-loud active galaxies. The nature of the observed jets in relation to the bulk flow is still unclear. In particular it is not clear whether the observations of parsec-scale jets using the very long baseline interferometric technique (VLBI) reveal wave-like structures that develop and propagate along the jet, or trace the jet flow itself. In this contribution I review the evidence collected during the last years showing that the ridge-lines of helical radio-jets do not correspond to observational artifacts. This conclusion was reached by studying …
In this paper we explore the dynamics of radiative axisymmetric MHD jets at high resolution using AMR methods. The goal of the study is to determine both the dynamics and emission properties of such jets. To that end we have implemented microphysics enabling us to produce synthetic maps of H$α$ and [S II]. The jets are pulsed either sinusoidally or randomly via a time-dependent ejection velocity which leads to a complicated structure of internal shocks and rarefactions as has been seen in previous simulations. The high resolution of our simulations allows us to explore in great detail the effe…
We investigate the linear and nonlinear evolution of current-carrying jets in a periodic configuration by means of high resolution three-dimensional numerical simulations. The jets under consideration are strongly magnetized with a variable pitch profile and initially in equilibrium under the action of a force-free magnetic field. The growth of current-driven (CDI) and Kelvin-Helmholtz (KHI) instabilities is quantified using three selected cases corresponding to static, Alfvenic and super-Alfvenic jets. During the early stages, we observe large-scale helical deformations of the jet correspondi…
We present the results of a numerical investigation of the spectra and light curves of the emission from the photospheres of long-duration gamma-ray burst jets. We confirm that the photospheric emission has high efficiency and we show that the efficiency increases slightly with the off-axis angle. We show that the peak frequency of the observed spectrum is proportional to the square root of the photosphere's luminosity, in agreement with the Amati relation. However, a quantitative comparison reveals that the thermal peak frequency is too small for the corresponding total luminosity. As a conse…
Extragalactic jets originating from the central supermassive black holes of active galaxies are powerful, highly relativistic plasma outflows, emitting light from the radio up to the gamma-ray regime. The details of their formation, composition and emission mechanisms are still not completely clear. The combination of high-resolution observations using very long baseline interferometry (VLBI) and multiwavelength monitoring provides the best insight into these objects. Here, such a combined study of sources of the TANAMI sample is presented, investigating the parsec-scale and high-energy proper…
The X-ray spectrum of the Galactic microquasar SS 433 contains a rich set of emission lines of highly ionized atoms of heavy elements whose significant Doppler shift leaves no doubt that they are produced in collimated relativistic jets of outflowing material. We have performed a systematic analysis of the high-resolution X-ray spectra obtained by the Chandra observatory to determine the parameters of the jets within the multitemperature model of their emission that self-consistently predicts the source's line and continuum spectrum. The spectrum of SS 433 at energies below 3 keV is shown to b…
GRB 170817A/GW 170817 is the first GRB clearly viewed far from the GRB jet's symmetry axis. Its afterglow was densely monitored over a wide range of frequencies and times. It has been modeled extensively, primarily numerically, and although this endeavour was very fruitful, many of the underlying model parameters remain undetermined. We provide analytic modelling of GRB afterglows observed off-axis, considering jets with a narrow core (of half-opening angle $θ_{\rm c}$) and power-law wings in energy per unit solid angle ($ε=ε_cΘ^{-a}$ where $Θ=[1+(θ/θ_{\rm c})^2]^{1/2}$) and initial specific k…
We study the angular dependence of the flux from partially synchrotron self-absorbed conical jets (proposed by Blandford \& K{ö}nigl). We consider the jet viewed from either a side or close to on axis, and in the latter case, either from the jet top or bottom. We derive analytical formulae for the flux in each of these cases, and find the exact solution for an arbitrary angle numerically. We find that the maximum of the emission occurs when the jet is viewed from top on-axis, which is contrast to a previous result, which found the maximum at some intermediate angle and null emission on-axis. W…
Simulations of active galactic nuclei (AGN) jets have thus far been performed almost exclusively using grid-based codes. We present the first results from hydrodynamical tests of AGN jets, and their interaction with the intracluster medium (ICM), using smoothed particle hydrodynamics (SPH) as implemented in the SWIFT code. We launch these jets into a constant-density ICM, as well as ones with a power-law density profile. We also vary the jet power, velocity, opening angle and numerical resolution. In all cases we find broad agreement between our jets and theoretical predictions for the lengths…
There are several lines of evidence indicating that the ultra-relativistic outflows powering gamma-ray bursts (GRBs) are collimated into narrow jets. However, these are indirect, and the jet structure is rather poorly constrained. What is more, the jet dynamics have still not been investigated in detail. It has been suggested that the observed variety between different long duration events, ranging from bright spectrally hard GRBs, to dimmer and spectrally softer X-ray flashes (XRFs) may be largely due to different viewing angles (or lines of sight) relative to rather similar relativistic jets…
Here, we demonstrate that polarization properties show a wide diversity depending on viewing angles. To simulate images of a supermassive black hole and surrounding plasma, we performed a full-polarimetric general relativistic radiative transfer based on three-dimensional general relativistic magnetohydrodynamics models with moderate magnetic strengths. Under an assumption of a hot-jet and cold-disk in the electron temperature prescription, we confirmed a typical scenario where polarized synchrotron emissions from the funnel jet experience Faraday rotation and conversion in the equatorial disk…
We investigate the emission properties that a large-scale helical magnetic field imprints on AGN jet synchrotron radiation. A cylindrically symmetric relativistic jet and large-scale helical magnetic field produce significant asymmetrical features in transverse profiles of fractional linear polarization, intensity, Faraday rotation, and spectral index. The asymmetrical features of these transverse profiles correlate with one another in ways specified by the handedness of the helical field, the jet viewing angle (theta_ob), and the bulk Lorentz factor of the flow (Gamma). Thus, these correlatio…
Polarization offers a unique view in the physical processes of astrophysical jets. We report on optical circular polarization observations of two famous blazars, namely 3C 279 and PKS 1510-089, at high linearly polarized states. This is the first time PKS 1510-089 is observed in optical circular polarization. While only upper limits can be extracted from our observing campaign, the non-detection of optical circular polarization allows us to provide meaningful constraints on their magnetic field strength and jet composition. We find that high-energy emission models requiring high magnetic field…
Structured jets are recently invoked to explain the complex emission of gamma ray bursts, such as GW 170817. Based on the accretion simulations, the jets are expected to have a structure that is more complex than a simple top-hat. Also, the structure of launching regions of blazar jets should influence their large scale evolution. This is recently revealed by the interactions of jet components in TXS 0506+056, where the jet is observed at a viewing angle close to zero. Observational studies have also shown an anti-correlation between the jet variability, measured e.g. by its minimum variabilit…
Numerical Simulations of Restarted Jets -- I. Dynamics
Inter-University Centre for Astronomy and Astrophysics（星际大学天文与天文物理中心）；INAF, Osservatorio Astrofisico di Torino（意大利国家天体物理研究所都灵天文台）；Istituto Nazionale di Astrofisica (INAF) - Istituto di Radioastronomia (IRA)（意大利国家天体物理研究所无线电天文研究所）；ASTRON, the Netherlands Institute for Radio Astronomy（荷兰射电天文研究所）；Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）
With this paper we introduce the concept of apparent structure of a GRB jet, as opposed to its intrinsic structure. The latter is customarily defined specifying the functions epsilon(theta) (the energy emitted per jet unit solid angle) and Gamma(theta) (the Lorentz factor of the emitting material); the apparent structure is instead defined by us as the isotropic equivalent energy E_iso(theta_v) as a function of the viewing angle theta_v. We show how to predict the apparent structure of a jet given its intrinsic structure. We find that a Gaussian intrinsic structure yields a power law apparent …
We present a numerical model developed to calculate observed fluxes of relativistic jets in active galactic nuclei. The observed flux of each turbulent eddy is dependent upon its variable Doppler boosting factor, computed as a function of the relativistic sum of the individual eddy and bulk jet velocities and our viewing angle to the jet. The total observed flux is found by integrating the radiation from the eddies over the turbulent spectrum. We consider jets that contain turbulent eddies that have either standard Kolmogorov or recently derived relativistic turbulence spectra. We also account…
The Perseus galaxy cluster is known to present multiple and misaligned pairs of cavities seen in X-rays, as well as twisted kiloparsec-scale jets at radio wavelengths; both morphologies suggest that the AGN jet is subject to precession. In this work we performed 3D hydrodynamical simulations of the interaction between a precessing AGN jet and the warm intracluster medium plasma, which dynamics is coupled to a NFW dark matter gravitational potential. The AGN jet inflates cavities that become buoyantly unstable and rise up out of the cluster core. We found that under certain circumstances preces…
The class of Double-Double Radio Galaxies (DDRGs) relates to episodic jet outbursts. How various regions and components add to the total intensity in radio images is less well known. In this paper we synthesize synchrotron images for DDRGs based on special relativistic hydrodynamic simulations, making advanced approximations for the magnetic fields. We study the synchrotron images for: Three different radial jet profiles; Ordered, entangled or mixed magnetic fields; Spectral ageing from synchrotron cooling; The contribution from different jet components; The viewing angle and Doppler (de-)boos…
We explore the use of SKA to deduce the physical parameters of kiloparsec-scale jet flows in radio galaxies. Jets in Active Galactic Nuclei are relativistic where they are first formed, but their speeds and compositions change as they propagate. It has long been known that kiloparsec-scale jets in radio galaxies can be divided into two flavours: strong (found in powerful sources, narrow and terminating in compact hot-spots) and weak (found in low-luminosity sources, geometrically flaring, unable to form hot-spots and terminating in diffuse lobes or tails). We have developed methods to model AG…
In this chapter we review some aspects of X-ray binaries, particularly those presenting steady jets, i.e. microquasars. Because of their proximity and similarities with active galactic nuclei (AGN), galactic jet sources are unique laboratories to test astrophysical theories of a universal scope. Due to recent observational progress made with the new generation of gamma-ray imaging atmospheric Cherenkov telescopes and in view of the upcoming km3-size neutrino detectors, we focus especially on the possible high-energy gamma radiation and neutrino emission. In connection with this, we also commen…
We present RadioAstron Space VLBI imaging observations of the BL Lac object S5 0716+71 made on January 3-4 2015 at a frequency of 22 GHz (wavelength $λ=1.3$ cm). The observations were made in the framework of the AGN Polarization Key Science Program. The source was detected on projected space-ground baselines up to 70 833 km (5.6 Earth diameters) for both, parallel hand and cross-hand interferometric visibilities. We have used these detections to obtain a full-polarimetric image of the blazar at an unprecedented angular resolution of 24 $μ$as, the highest for this source to date. This enabled …
High-resolution very long baseline interferometry (VLBI) radio observations have resolved the detailed emission structures of active galactic nucleus jets. General relativistic magnetohydrodynamic (GRMHD) simulations have improved the understanding of jet production physics, although theoretical studies still have difficulties in constraining the origin and distribution of jetted matter. We construct a new steady, axisymmetric GRMHD jet model to obtain approximate solutions of black hole (BH) magnetospheres, and examine the matter density distribution of jets. By assuming fixed poloidal magnet…
Last and nearest GRB-XRF 080109 has been an exceptional lesson on GRB nature. After a decade (since 25 April 08) we know that Supernovae may often contain a Jet. Its persistent activity may shine on axis as a GRBs. Such a persistent, thin beamed gamma jet may be powered by either a BH (Black Holes) or Pulsars. Late stages of these jets may loose the SN traces and appear as a short GRB or a long orphan GRB (depending on jet angular velocity and view angle). XRF are peripherical viewing of the jets. These precessing and spinning gamma jet are originated by Inverse Compton and-or Synchrotron Radi…
We conducted radio detection observations at 8.4 GHz for 22 radio-loud broad absorption line (BAL) quasars, selected from the Sloan Digital Sky Survey (SDSS) Third Data Release, by a very-long-baseline interferometry (VLBI) technique. The VLBI instrument we used was developed by the Optically ConnecTed Array for VLBI Exploration project (OCTAVE), which is operated as a subarray of the Japanese VLBI Network (JVN). We aimed at selecting BAL quasars with nonthermal jets suitable for measuring their orientation angles and ages by subsequent detailed VLBI imaging studies to evaluate two controversi…
Our view of the properties of extragalactic radio jets and the impact they have on the host galaxy has expanded in the recent years. This has been possible thanks to the data from new or upgraded radio telescopes. This review briefly summarises the current status of the field and describes some of the exciting recent results and the surprises they have brought. In particular, the physical properties of radio jets as function of their radio power will be discussed together with the advance made in understanding the life-cycle of radio sources. The evolutionary stage (e.g. newly born, dying, res…
